Projects relate to studies in experimental animals (rat) and man concerning influences of aging on cell surface and intracellular hormone receptors, the adenyl cyclase system, and the male reproductive system. The hormones involved are catecholamines, polypeptides, glucocorticoids and testosterone. Aspects of the biochemistry of the adenyl cyclase system are included. A major effort is directed toward relating biochemical changes at the molecular level to altered physiological responsiveness.